The present invention is directed to a dragline apparatus, and more particularly, to a bucket that may be used in connection with a dragline apparatus having front and rear hoist lines connected to the bucket.
A dragline apparatus employs a series of lines, such as chains or ropes, to advance and control an earth-moving bucket. A typical bucket of the prior art is supported in part by a pair of hoist lines which are attached to opposite side walls of the bucket. An example of a conventional dragline apparatus is shown in FIGS. 4A and 4B. (See, e.g., U.S. Pat. No. 5,992,061.) The hoist lines are, in turn, coupled through a linkage assembly to one or more lift lines which extend down from an overhead boom. A dump line is connected to the front end of the bucket and to a drag line or drag rope (referred to herein as a drag rope) used for pulling the bucket through the ground. A medial portion of the dump line is wrapped about the sheave of a dump block which is also connected through a linkage assembly to the lift lines. The tension applied to the dump line by the drag rope causes the dump line to raise the front of the bucket. Release of the tension then permits the front of the bucket to tip forward and dump the accumulated load.
The production capacity of a dragline apparatus, or the amount of material that may be removed by the dragline apparatus over a given period of time, depends on several factors. One factor is the capacity of the bucket, which in turn depends on the weight of the bucket. It is desirable to decrease the weight of the bucket so as to allow more material to be carried. However, it is often necessary to provide heavy wear protection and to use heavy chains because of the wear and stress encountered by the bucket during operation. Production capacity is also related to the cycle time, which is the amount of time required to fill and empty a bucket. Reducing the cycle time will allow a bucket to carry more material over a given period of time, thus increasing production capacity.
A conventional dragline apparatus has the advantage of requiring only two winches to control movement of the bucket. Hoisting is controlled by a hoist winch, which controls movement of the hoist lines. A second winch is used to control the drag rope. Tension on the drag rope and hoist line is used to control the attitude of the bucket.
Nevertheless, the conventional dragline apparatus has several disadvantages. One of the primary problems with the current dragline apparatus is that there are many places where the bucket cannot be picked up without spilling the contents of the bucket. This is due to the relationship between the drag rope and the hoist line and the included angle therebetween. When the included angle between the drag rope and the hoist line is less than 90xc2x0, it is very difficult to pick up the bucket unless an extremely short dump line is used. However, when a very short dump line is used, the tension on the dump line when the bucket is carried can be extremely great such that damage is done to the dump line, dump block, dump block connection hardware, arch, and many other associated rigging components. The inability of the conventional dragline apparatus to pick up the bucket over a wide range of locations limits production capacity.
Buckets must also be built to withstand enormous stresses, but this increases the weight of the bucket. In order to hoist such buckets, tension is maintained on the drag rope while tension is applied to the hoist line. Preferably, the front of the bucket begins to lift first, followed by the entire bucket. This has the preferential effect of capturing the loose material, which is heaped at the front of the bucket, rather than having it slough off the front as the bucket is picked up. Unfortunately, this method of lifting has the negative effect of rotating the heel of the loaded bucket through the material every time it is picked up. Accordingly, the heel portion of the bucket is typically substantially reinforced with wear protection. In addition, the inability to pick up the bucket when the included angle between the drag rope and hoist rope is less than 90xc2x0 often results in the loaded bucket being dragged up the slope to a point at which the bucket can be hoisted. Accordingly, a substantial amount of wear protection is required for the bucket. This need for substantial wear protection has the effect of decreasing the capacity of the bucket.
A conventional bucket also typically has a heavy, reinforced front arch, which provides the connection point to the dump line. Conventional buckets also use a drag chain interconnecting the bucket with the drag rope. One reason for using a chain is to form a catenary to provide clearance during dumping. Both the reinforced arch and drag chains add additional weight, again reducing production capacity.
Yet another disadvantage of the conventional rigging of a dragline apparatus is the requirement of a dump block and its attendant rigging. This adds additional weight and complexity to the apparatus.
Accordingly, there has been at least one attempt to overcome some of these disadvantages by providing a rigging for a dragline apparatus which provides a separate front hoist line and eliminates the dump block and its rigging. Australian Patent Document No. AU-A-34502/89 discloses a dragline apparatus and method of excavation in which the dump rope is omitted and instead replaced with a front hoist line which is attached to the front end of the excavator bucket.
However, it has been found by the present inventors that a conventional bucket will not perform well with such a modified rigging. FIG. 5A shows calculated loads on the drag rope D, front hoist line F, and rear hoist line R connected to a conventional bucket using such a modified rigging. The loads are calculated for a conventional bucket with side trunnions as shown in FIGS. 4A and 4B, and with the front hoist line connected to the anchor on the arch. The calculation assumes a full bucket load and a 15 degree carry attitude, with the bucket located 20 feet below the level of the tub. The calculation shows several drawbacks of a conventional bucket. First, with a calculated negative load in the front hoist rope, it is unlikely that the bucket could be dumped inside of 150 feet from the tub. Further, it is unlikely the bucket would dump well even further out, as there would be insufficient tension to overcome the friction and inertia of the hoist lines within the boom to effect a clean dumping action. The failure to completely dump the load results in a loss of carrying capacity. The material carried back eliminates part of the bucket capacity that would otherwise be available. This is particularly a problem when dumping wet, sticky material. Second, the calculation shows that the average load in the front and rear hoist ropes is far different. The result will be an increased rate of wear on the rear hoist rope relative to the front hoist rope.
Accordingly, what is desired is a bucket for use with a dragline apparatus having a modified rigging system including a front hoist line and a rear hoist line, in which the bucket provides clean dumping over a wide range of locations, that allows efficient dumping, that conserves energy during dumping, that allows for a reduced cycle time, that increases the amount of material that may be carried by the bucket, and that may be operated in an efficient manner.
The invention overcomes the aforesaid drawbacks by providing a dragline apparatus that enables use of an independently controlled front hoist line and a rear hoist line, a modified bucket for such a dragline apparatus, and a method for operating such a dragline apparatus.
In a first aspect of the invention, a dragline apparatus comprises a housing having a front hoist winch and a front hoist line, a rear hoist winch and a rear hoist line, and a drag winch and a drag rope. The front hoist line and the rear hoist line are supported by a boom extending from the housing. A bucket has side, rear and bottom walls, in which the bottom wall terminates in a forward lip adapted to be equipped with excavating teeth. The bottom wall adjacent to the rear wall is contoured to form a heel. Each of the side walls at the forward end have a connection point for attachment of a drag rope. The front hoist line is connected to the forward end of the bucket. The rear hoist line is connected to the bucket at a location adjacent to the heel, and below the average loaded center of gravity of the bucket.
This aspect of the invention provides a number of advantages. In contrast to a conventional dragline apparatus, in this aspect of the invention the rear connection point for the rear hoist line is moved to the rear of the bucket. In addition, unlike a conventional dragline apparatus, the front hoist line is not connected to the arch, but instead is connected to the forward end of the bucket. This results in a bucket that distributes the load more evenly between the front hoist line and the rear hoist line. The carrying capacity of the bucket is improved, as well as the dumping ability. Equalizing the tension between the front and rear hoist lines also causes the lines to wear at the same rate, thus allowing the same size lines and connectors to be used and decreasing the time and expense associated with changing worn out lines.
In another aspect of the invention, a bucket for use with a dragline apparatus comprises side, rear and bottom walls. The bottom wall terminates in a forward lip adapted to be equipped with excavating teeth. The bottom wall adjacent to the rear wall is contoured to form a heel. Each side wall has at the forward end a connection point for attachment of a drag rope. The bucket has at least one rear connection point for a rear hoist line located adjacent to the heel. Each side wall has at the forward end a respective front connection point for a respective front hoist line. The bucket has a first distance between the front connection point and an average loaded center of gravity, and a second distance between the rear connection point and the average loaded center of gravity, such that the first distance is less than the second distance.
By locating the connection points for the front hoist line and rear hoist line in this manner, the load carried by the front hoist line and rear hoist line is distributed in a fashion that allows dumping over a wider range of locations and that also distributes the load more evenly between the front and rear hoist lines. The bucket achieves improved capacity by reducing the weight of the bucket and associated rigging. In addition, the cycle time may be reduced due to quicker dumping of the bucket, and due to quicker return of the bucket after dumping due to reduced weight of the bucket.
In another aspect of the invention, a method is provided for operating a dragline apparatus. A front hoist line and rear hoist line, and a front hoist winch and a rear hoist winch are provided. A bucket is provided having a body comprising side, rear and bottom walls. The bottom wall terminates in a forward lip adapted to be equipped with excavating teeth. The bottom wall adjacent to the rear wall is contoured to form a heel. Each of the side walls at the forward end has a connection point for attachment of a drag rope. A rear hoist line is provided which is connected to the body at a location adjacent to the heel. A front hoist line is provided which is connected to the body at the forward end of the body. The bucket is operated by independently changing the length of the front hoist line while simultaneously independently changing the length of the rear hoist line.
This aspect of the invention provides the advantage of allowing a wide range of motion for the bucket. By independently operating the front hoist and rear hoist lines, the bucket may be picked straight up, thereby reducing wear at the heel portion of the bucket. The efficiency of dumping may be improved, by simultaneously paying out the front hoist line while pulling in the rear hoist line. This may reduce the cycle time and also reduce the amount of energy expended during the dumping operation. In addition, independent operation of the rear and front hoist lines can allow the bucket to be dumped rearward by use of shortening the front hoist line and lowering the rear hoist line. Alternatively, the bucket may be dumped sideways by selectively changing the lengths of the hoist lines. Independent control of the front hoist and rear hoist lines also makes the bucket more adaptable to different digging conditions, improving chopping, bench cutting, rehandle and short dumping.
In another aspect of the invention, a dragline apparatus comprises a housing having a drag line winch, a front hoist winch, and a rear hoist winch. A boom extending from the housing supports the front hoist line and the rear hoist line, which are connected respectively to the front and rear of an excavator bucket. The drag line is connected to the forward portion of the excavator bucket. A coupling mechanism interconnects the front hoist winch and the rear hoist winch, so that the front hoist winch may be unwound at a rate that is proportional to the rate at which the rear hoist winch is wound.
In yet another aspect of the invention, a dragline apparatus comprises a housing having a drag rope winch, a front hoist winch, and a rear hoist winch. A boom extending from the housing supports the front hoist line and the rear hoist line, which are connected respectively to the front and rear of a bucket. The drag rope is connected to the forward portion of the bucket. The housing has a drive shaft connected to a drive transmission interconnecting the front hoist winch and rear hoist winch. A coupling mechanism is operatively engaged with the drive transmission to control the rotation of the front hoist drum and the rear hoist drum. In one embodiment, the coupling mechanism is a second differential. In an alternative embodiment, the coupling mechanism is a sliding rack.
This aspect of the invention has the advantage of providing a mechanical assembly for control of the two independent hoist ropes. The invention eliminates the need for complicated software to run the dragline apparatus, which may be difficult to service in remote mining locations. In contrast, a mechanical assembly may be serviced by the crew that is present at the mining operation.
The foregoing and other features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.